1. Field of the Invention
The present invention relates to a power unit including an engine, a belt transmission driven by the engine, and a second transmission, such as a gear transmission, driven by the belt transmission, wherein the power unit is adaptable to a vehicle, especially, a multi-wheel drive vehicle such as a four-wheel drive vehicle.
2. Related Art
As disclosed in each of JP H02-200526A, JP H10-297295A and U.S. Pat. No. 7,377,351, a typical conventional power unit for a multi-wheel drive vehicle, such as a four-wheel drive utility vehicle, includes an engine, a belt transmission driven by the engine, and a second transmission having first and second output portions for respective front and rear wheel axles and driven by the belt transmission. In this power unit, an engine output shaft of the engine has a horizontal axis in a fore-and-aft direction of a vehicle. The second transmission is disposed on one of the right and left sides of the engine. Transmission shafts of the second transmission have respective horizontal axes in the fore-and-aft direction of the vehicle.
One of the transmission shafts of the second transmission is a transmission input shaft serving as an input shaft of the transmission shafts. The engine output shaft and the transmission input shaft have end portions projecting forward or rearward from the engine and the second transmission in the vehicle. The belt transmission is disposed on one of the front and rear sides of the engine and the second transmission so as to drivingly connect the end portions of the engine output shaft and the transmission input shaft to each other.
More specifically, in the belt transmission disposed on the front or rear side of the engine and the second transmission, a drive pulley is provided on the end portion of the engine output shaft, a driven pulley is provided on the end portion of the transmission input shaft, and a belt is looped over the drive and driven pulleys.
In the typical conventional power unit, a belt transmission casing is provided therein with a belt transmission chamber incorporating the belt transmission, including the drive and driven pulley and the belt. A second transmission casing separated from the belt transmission casing is provided therein with a second transmission chamber incorporating the second transmission. The end portion of the transmission input shaft to be drivingly connected to the belt transmission is extended outward from the second transmission casing and into the belt transmission chamber of the belt transmission casing.
Generally, the belt transmission casing is constituted by joining divisional casing members for convenient maintenance of the belt transmission in the belt transmission chamber. In this regard, for maintenance of the belt transmission, one divisional casing member can be separated from another divisional casing member so as to easily expose the belt transmission.